Over the years, infusion pumps have been used to deliver a wide variety of medication types and fluids, intravenously, to medical patients. Infusion pumps used to deliver intravenous fluids and solutions for a wide variety of medical therapies including chemotherapy, antiviral and antibiotic therapy, and also include intravenous introduction of blood, saline solutions, glucose solutions and various other solutions comprising pharmaceuticals.
In many situations, a patient may require multiple daily therapies, intermittent infusion, or a slow and continuous introduction of medicament liquid into the patient's system. Moreover, certain therapies require medicament liquid or pharmaceutical solutions to be infused over a particular period of time which may range anywhere from about 30 minutes to about several hours, for a therapeutic dose. It is therefore very important that these medicament liquid or pharmaceutical solution doses be administered completely and with a highly accurate introduction rate (flow rate).
Currently, a variety of devices exist that are able to deliver medicament liquids and pharmaceutical solutions intravenously to a patient. In the past few years, certain of these devices have offered some degree or portability, but the most widely utilized of these devices typically require a patient to be confined to a bed, thus limiting the options available for patients who are able to be ambulatory.
So called ambulatory infusion pumps are gaining currency in medical technology, given the trend towards shorter hospital stays and increasing reliance on out-patient and home care treatment. Such ambulatory devices typically function on an infusion pump delivery principle which pumps a medicament liquid or other IV solution into the patient. The pressure developed by the infusion pump is designed to overcome the resistance of the patient's internal pressure and include regulators or restrictors in the IV tubing set to attempt to control the rate of flow of the IV solution into the patient.
The prior art discloses several types of ambulatory infusion pumps which attempt to approximate reasonable levels of accuracy in administering IV solutions. For example, it is common to pressurize a container filled with a medicament liquid or IV solution by transmitting a hydrostatic or gas pressure developed in an external or internal gas-filled bladder to the IV solution container. By maintaining a constant pressure in the bladder, it was hoped that the bladder would exert (transmit) a constant pressure to the IV solution container, thereby developing a constant flow rate of medicament liquid at the point of infusion. However, as is well understood in the art, the gas pressure inside an expanding bladder necessarily decreases as the bladder's internal volume increases, in accordance with Boyle's Law.
In order to obtain some measure of accuracy and control in IV solution delivery, the various infusion pump systems that generate their own pressure to overcome patient pressure resistance must contain some means for controlling a fluid flow rate at the various pressures and flow rates required by multiple therapeutic applications. Common stationary gravity feed units provide some limited control possibilities by adjusting the height of a medical container above the point of infusion, but this technique requires additional apparatus upon which to hang a medical container, thus limiting the unit's portability. Certain electromechanical infusion pumps, such as volumetric peristaltic or piston-cylinder pumps provide for relatively accurate delivery, but have rather large power requirements which necessitates frequent battery replacement.
In the more common elastomeric-type infusion pump devices, the elastomeric pumps use the pressure of an expanding elastomeric element to push an IV solution through a rate controlling orifice or a constrictive clamp. While relatively simple, this technique is only useful to provide a constant flow rate if the pressure head of the liquid entering the rate controlling orifice is generally constant. As soon as the pressure varies, the IV solution flow rate will necessarily change in response.
In addition to these disadvantages, contemporary ambulatory infusion pumps also require IV solutions or medicament liquids to be hosted in special containers which are not necessarily adapted to the use of standard, pre-filled single dose IV solution containers. Where contemporary infusion pumps are not able to be used with a standard IV solution container, the medicament liquid desired to be infused must be separately compounded and then introduced into the specialized infusion pump container. This practice, of course, has implications for the sterility of the medicament solution since the solution must pass through additional handling steps in the preparation and transfer process, prior to being introduced to a patient. The requirement to compound and transfer the IV solution is time consuming and increases the risk of contamination.
Further, in order to minimize the various disadvantageous features of conventional ambulatory infusion pumps, certain prior art-type devices have incorporated additional systems, at a substantial penalty and complexity and added cost, to address variable flow rates and non uniform pumping pressures. For example, U.S. Pat. No. 5,348,539 discloses an infusion pump with an inflatable chamber, terminated in a diaphragm which expands and contracts under fluid pressure in order to compress the sidewalls of an IV solution container. A fluid, in the form of a liquid, is transferred to and from the inflatable chamber through a reservoir. The system includes a complex valve arrangement by which the fluid is introduced into the chamber and withdrawn therefrom. The overall system is controlled by a electronic circuitry which includes pressure sensors in the inflatable chamber and logic circuitry which controls a reversible fluid pump which moves the liquid between the reservoir and the inflatable chamber, the whole monitored and controlled by a suitable micro-controller IC chip. While relatively compact and accurate, this system is also highly complex, expensive and requires a great deal of electrical power to operate.
An additional prior art-type system is disclosed by U.S. Pat. No. 5,106,374 in which gas pressure uniformity is addressed by providing a housing with a series of cavities in which there are provided expandable pressure regulator tubes. The regulator tubes are interconnected through a series of passageways, connectors, etc. to an inflatable, flexible, substantially non-stretchable diaphragm provided in yet another housing cavity. The diaphragm provides the pressure source against an IV solution container with the expandable pressure regulator tubes defining a pressure reservoir. The system becomes charged when the regulator tubes are expanded by a, for example, compressed gas source. Once the infusion process is initiated, the regulator tubes gradually deflate forcing the non-expandable diaphragm against a flexible IV solution container. Medicament is infused at a substantially steady rate into the patient until the medicament bag has been emptied. While again rather compact and reasonably accurate, this particular system is disadvantageous in terms of component complexity and lack of flexibility.
Accordingly, while various systems are known for providing intravenous delivery of fluids to an ambulatory patient, there is no single system that is reusable, is able to be used with standard IV solution containers as opposed to specialized disposables, is simple to operate, includes a minimum of component parts, requires no source of electrical energy, and is able to store and deliver anywhere from about 50 to about 250 mL of medication using standard manufacturers' flexible drug containers, at flow rates of from about 50 mL to about 200 mL per hour.